Roller members are used in a conveying system for sheet materials (paper, plastic sheets, and any other sheets) in copying machines and printers. This type of roller members are sometimes produced in the process of press-fitting a roller portion molded with, for example, a synthetic rubber material, into a roller shaft. This method may lead to an increase in production cost because of its large number of processes.
Flange portions, which serve as register marks for positioning a rubber roller portion on a roller shaft in the axial direction when the roller portion is press-fitted in the roller shaft, are disposed at both ends of the roller portion, and the positions of the rubber roller portion is finely adjusted so that the roller portion is positioned inside the two flange portions. However, such a method of production can make clearance between the two flange portions and the rubber roller portion during the press-fitting process, leading to a decrease in the accuracy of the mounting position in the axial direction, or can deform the rubber roller portion, leading to a decrease in the accuracy of the external shape. Thus, to increase the coaxial accuracy of the roller shaft and the rubber roller portion after the press-fitting, the outer circumference needs to be ground, thus increasing the cost. Furthermore, because of the positioning only with press-fitting, the strength of bonding between the roller portion and the roller shaft is so insufficient that the roller portion is displaced.
In view of the above, two-color molding is proposed (for example, PTL 1) for a sheet-conveying roller member of a copying machine or any other machine. The roller member has a friction material around the outer circumference of a roller main body. The friction material and the roller main body are integrally molded by two-color molding. The roller member disclosed in PTL 1 is molded such that the friction material is integrally formed between a plurality of branches disposed substantially at regular intervals around the outer circumference of the roller member. The structure disclosed in PTL 1 in which the friction material and the roller main body are two-color (double) molded eliminates the need for the process of assembling the friction material and the roller main body in a downstream operation.